Strapping machines, both automatic and manual, are known for securing straps around loads.
Steel strap can be used to secure loads, such as structural steel members, pipe, steel coils, metal plates and like materials that could otherwise overload or compromise the integrity and/or strength of plastic strap material. Typically, a hand-held tensioning tool is positioned on the load and the strap is positioned in the tool and tensioned. A seal is then applied to the strap to secure the tensioned strap around the load.
The seals can be of the crimp-type, in which a seal element is positioned around overlying courses of strap material and crimped onto the strap. Alternately, a crimp-less seal, which uses a set of interlocking cuts in the strap can be used. Alternately still, a spot weld can be used to join the two ends of the strap. The hand-held tools can be fully manual or can be powered, such as by pneumatic motors, electric motors or the like.
Welding steel strap is also known, and is currently done using spot weld and inert-gas (i.e., TIG) welding processes to join feed coils together to maintain a continuous manufacturing process.
Haberstroh, US Publication 2013/0276415, commonly assigned with the present application discloses a modular steel strapping machine that applies, tensions and welds a strap to itself in an end-to-end weldment around a load. In order to tension the strap, a device, for example, a self-actuating tension head, such as that disclosed in Bell, Jr., U.S. Pat. No. 8,701,555 draws tension in the strap during the strapping cycle.
During the strapping cycle, following tensioning the strap, the tension on the strap must be relaxed a short predetermined distance so that the welding cycle can properly function. Although the tension head in Bell functions well in operation, it does not provide a way in which the strap tension can be relaxed (or the strap rolled back) for welding.
Accordingly, there is a need for an tension head for a strapping machine that draws tension in steel strap during the strapping cycle and secures the strap as required for proper function of the strapping machine, and specifically for the feeding and welding cycles of the strapping machine. Desirably, such a tension head provides a measured amount of rollback so that the welding cycle is properly carried out and resets to properly position the tension head for subsequent operations.